Debris flow drainage canal based on cascade antiscour notched sill group and application thereof

ABSTRACT

A system of debris-flow drainage canal with cascaded sills is provided, which allows a high-efficient and low-cost realization of debris flow drainage and scour prevention. The canal contains two converging walls and a series of scour prevention sills, which are laid between the two converging walls. The sills are embedded to a certain depth and are evenly spaced and symmetrical to the centre line of the canal to form a cascaded structure for scour prevention. The drainage canal&#39;s width is 2 times wider than the sill&#39;s horizontal length along the cross-section. Compared with the prior art, this system can drain off a wide variety of flows from debris flow to flood and prevent debris-flow siltation even on a gentle slope. This system has a much higher stability and longer life of service. Moreover, this system can maintain the aquatic habitat in gullies and contribute to ecological restoration.

FIELD

This disclosure relates to the field of debris flow drainage technology.In particular, the disclosure relates to a system of drainage canal withscour-prevention cascaded sills, for the purpose of draining off lowviscosity debris flow, water-rock flow and flood through dissipatingflow energy by soft streambed.

BACKGROUND

Debris flow is characterized by high inertia, strong transportingability and great impact force because of its composition of elasticsoil. Strong erosion caused by debris flow can bring dramatic changes togully bed, making gully bed revealed and bank collapse, which in turnsupplies solid materials to the debris flow and magnifies the damage.Thus, debris flow brings severe harms to towns, villages, roads, canals,electric and communication lines, farmlands and forests. Therefore, itwould have great significance on society, economy and ecologicalenvironment to invent new structure type that can effectively controlthe scour caused by debris flow, reduce damage and enhance safety ofdownstream protecting objects.

In recent years, the utilization of debris flow fans has increased withthe growing of construction of many large capital construction projects.It is becoming more important to control scour and siltation of debrisflow. Among numerous debris flow basins, the occurrence probability ofdiluted debris flow, transitional debris flow and floods is high. Thus,it is urgent to develop new drainage canal that can meet the drainagerequirement of these kinds of debris flows.

The traditional entirely lined canal is usually of high cost but has ashort life due to the extremely strong erosion by debris flow. Thecurrently used canal with transverse throughout sills is generallyapplied in steep slope gully. When the slope gradient is smaller than5%, the canal will be silted notably and the drainage effect is verypoor. In perennial streams, the entirely lined canal and transversethroughout sills would break the connection between upstream anddownstream aquatic organisms, thereby going against ecologicalrestoration of the gully.

The Patent Application No. 200910058217.7, directed to Applicants'previous research achievement, discloses a drainage canal withcrisscross-spurs structures to drain spreading gradation fluid and keephydraulic connection in gullies for the benefit of ecologicalrestoration. However, the crisscross-spurs structures may cause backflow and threaten the safety of canal walls. Moreover, strong back flowmay lead to energy dissipation and sediment deposition. Reducing thelength of sill is effective in decreasing back flow in gullies withgentle slope, but this decreases the stability of the walls. It will beof high cost to reinforce the walls' foundation.

SUMMARY

The purpose of this invention is to provide a low cost drainage systemof canal with cascaded sills. This approach can implement safe andsmooth drainage of a variety of flows, keep dynamic balance betweenerosion and siltation, maintain the habitat of water living in gullies,and help ecological restoration. Furthermore, this approach can fullyensure the stability of the side walls in view of the centripetalconverging flow effect and avoid siltation even when the slope is small,making the drainage canal work for a longer time.

To achieve the above purpose, among others, the following exemplarysolution is provided by the invention.

An embodiment of the invention relates to a debris-flow drainage canalbased on scour prevention cascaded sills, which includes two flowconverging walls and a series of scour prevention cascaded sills. Theseries of scour prevention cascaded sills are placed between the twowalls, connected to the walls and utilized together with the walls. Thecascaded sills are made of a number of scour prevention sills, which areplaced with a certain embedded depth and each two steps are distributedwith a certain space. Each two sills are laid between the two wallssymmetrically with respect to the centre line of the drainage canal, andmake up a step of the scour prevention cascaded sills. The drainagecanal's width D (i.e., the distance between the two side walls) is 2times wider than the sill's horizontal length B along the verticaldirection of the wall (i.e., the sill's projected length in the verticaldirection of the wall), meeting the requirement of D>2 B. Stateddifferently, only one end of each sill is connected to the side wall,without crossing the canal, and the sills are laid between the two wallssymmetrically with respect to the centre line of the canal and make up asymmetric-form step of the scour prevention cascaded sills, Thissymmetrical structure can maintain full aquatic organism connection ingullies and is beneficial to the ecological restoration; thissymmetrical structure can also ensure the stability of the side wallsand avoid siltation even on a gentle slope, and work for a long time.

The sill's horizontal length B along the vertical direction of the wallis 1/10˜½ of the drainage canal's width D, meeting the requirement of1/10 D≦B<½ D; the greater the gully's longitudinal slope is, the longerthe sill's horizontal length B should be. This helps keep said sills'quantities as few as possible.

The sill inclines at an angle a at its connection to the wall andinclines to the downstream direction; i.e., the sill's connection end isupstream with respect to the other end. The angle α is between 45°˜75°.The greater the gully's longitudinal slope is, the larger the angle αshould be. This inclined structure contributes to converging flow.

Along the vertical direction of the side wall, the central portion ofthe sill is lower and the sides adjacent the wall is higher, Thetransverse slope 1:n, which is the sill's height difference h dividesthe sill's horizontal length B along the vertical direction of the wall,is 1:4˜1:20, in other words, 1:n=h: B. This structure of lower in thecentre than at the sides is used to improve converging flow and bottomturbulence, which is helpful to energy dissipation.

Along the vertical direction of the wall, the sill's top width b₁<thebottom width b₂, and the downstream side is vertical, while the upstreamside inclined. The sill's top width b₁ is 0.6˜1.5 m and bottom width h₂is 1.0˜2.0 m, and the upstream side's slope 1:m (which is upstreamslope's height H₁ divides (b₂−b₁)) is 1:0.4˜1:1, in other words, 1:m=H₁:(b₂−b₁). This structure of narrow top and wide bottom stabilizes thesill under the impact force of debris flow.

To build the drainage canal, the structure of grouted stone masonry,concrete, reinforced concrete, protection lead gabion can be used. Thespace L between each two steps of the scour prevention cascaded sills is8.0˜25.0 m, and the sill's embedded depth H is 1.5˜2.5 m. A reasonableembedded depth and space can keep the sill and side wall safe.

The drainage canal, which provides both energy dissipation effect inview of the longitudinal soft foundation and centripetal converging floweffect in view of the symmetrical sills, is particularly appropriate forpreventing and controlling diluted debris flow, water-rock flow andfloods with longitudinal slope 3%˜12%. Due to the sill's centripetalconverging flow effect, the side walls' stability can be ensured andstronger scour can be achieved to avoid siltation when the longitudinalslope is gentle, thereby ensuring long operation period.

An embodiment of the invention, based on the energy dissipation effectof soft foundation and centripetal converging flow effect of symmetricalsills and side walls, deals with the alternate effects of downwarderosion and siltation by fluid to prevent and control diluted debrisflow, water-rock flow and floods. When the flow rate is big, theembodiment dissipates internal kinetic energy in fluid by mean ofmaterial interchange between the lower turbulence and the upperdescending current in debris flow (or flood), thereby avoiding downwarderosion. When the flow rate is small, the embodiment prevents siltationin view of the scour effect by the centripetal converging flow,implements the dynamic balance of downward erosion and siltation, anddrains debris flow safely and smoothly. The symmetric structure iscapable of regulating the balance of downward erosion and siltation ingully, reducing debris-flow erosion, preventing siltation in gully,decreasing the costs and maintenance of operation, and ensuring thesafety of downstream protected objects. The drainage canal can be builtmainly on debris flow fans, leading debris flow into the designedregions according to the designed flow velocity and direction.

The advantages of the invention include, but are not limited to, thefollowing. More than 15% cost can be saved compared with the entirelylined canal, which in turn favors operation management. When thegradient of gully bed is gentle, better effect for preventing siltationand lower cost can be achieved compared with the transverse throughoutsills, and the drainage demand can still be satisfied when several kindsof fluid varying from diluted debris flow to flood occur in the samebasin. Considering the disclosure of Application Number 200910058217.7(A debris-flow drainage canal with indented-sill), this invention cannot only effectively carry on the advantages of ecological protection,but also avoid scouring the foundation of the side walls because of thecentripetal converging flow effect of the symmetrical sills, which wouldfully ensure the stability of the walls. In addition, there can bestronger scour to avoid siltation when the longitudinal slope is gentle,ensuring that the canal safely run for a long time.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a longitudinal profile of scour prevention cascadedsills;

FIG. 2 illustrates a top plan view of an embodiment of the invention;and

FIG. 3 illustrates a lateral profile of the embodiment.

The labels in the figures are shown as follows: 1 the scour preventioncascaded sill 2 the flow converging side wall; B horizontal length ofthe sill along the vertical direction of the wall; D width of thedrainage canal; α inclined angle of the sill; b₁ top width of the sillb₂ bottom width of the sill; H embedded depth of the sill; L distancebetween each two steps of the scour prevention cascaded sills; H heightdifference between the two ends of the sill; H₁ height of upstreamincline; 1:n the transverse slope; and 1:m the upstream side's slope.

DETAILED DESCRIPTION OF EMBODIMENTS

The exemplary embodiments the invention are now described with referenceto the figures.

Exemplary Embodiment I

As shown in FIGS. 1-3, the valley area is 2.0 km² and the slope ofdebris fan is 12%, considering diluted debris flow, water-rock flow andflood under designed standard. The debris flow drainage canal can bebuilt on the fan, including side walls 2 and scour prevention cascadedsills which are laid between the two walls, being connected to them andused together with them. Each two steps of the cascaded sills aredistributed with a certain space, and are made up of a number of scourprevention sills 1 with a certain embedded depth. The space L is 8.0 m,and the embedded depth is 2.5 m.

The sills are laid between the two walls symmetrically with respect tothe centre line of the canal, and make up a symmetric-form step of thescour prevention cascaded sills. The drainage canal's width D is 2 timeswider than the sill's horizontal length B along the vertical directionof the wall. Under the P_(2%) designed standard, the discharge of debrisflow in the canal is 28.0 m³/s; D is set as 3.0 m, B as 1.2 m, and α as75°.

Along the vertical direction of the walls 2, the sill 1 is shown aslower at the center and higher near the wall. The transverse slope 1:nis designed as 1:4. Along the vertical direction of the walls 2, the topwidth b₁ of the sill 1 is 0.6 m, and bottom width b₂ is 1.0 m. Thedownstream side is vertical, while the upstream side inclined. Theupstream side's slope 1:m, which is upstream slope's height H₁ divides(b₂-b₁), is 1:0.4, and H₁ is 1.0 m.

Exemplary Embodiment II

As shown in FIGS. 1-3, the valley area is 20.0 km² and the slope ofdebris fan is 3%, considering water-rock flow and flood in designedstandard. Beside the same as embodiment I, the differences are in that:the space L is 25.0 m and the embedded depth is 1.5 m.

Under the P_(2%) designed standard, the discharge of debris flow in thecanal is 100.0 m³/s. Set D as 16.0 m, B as 1.6 m, and α as 45°; thetransverse slope 1:n is 1:20, the top width b₁ of the sill 1 is 1.5 m,and the bottom width b₂ is 2.0 m; the upstream side's slope 1:m is 1:1,and H₁ is 0.5 m.

1. A debris flow drainage canal based on scour-prevention cascaded sillscomprises: two flow-converging walls; and a plurality of sills with apredetermined embedded depth, the plurality of sills being disposedbetween and connected to the walls, wherein the sills are evenly spacedand symmetrical with respect to the centre line of the canal, and thewidth D of canal is at least 2 times wider than the length B of thesills, meeting the requirement of D>2 B.
 2. The debris flow drainagecanal according to claim 1, wherein the horizontal length B of the sillsalong the vertical direction of the walls is 1/10˜½ of the drainagecanal's width D, meeting the requirement of 1/10 D≦B<½ D.
 3. The debrisflow drainage canal according to claim 1, wherein an angle is formedbetween the walls and one end of the sills connected to the walls, andthe other end of the sills inclines to a downstream direction.
 4. Thedebris flow drainage canal according to any one of claims 1-3, whereinalong the vertical direction of the walls, the sills presents lower atthe center and higher near the walls.
 5. The debris flow drainage canalaccording to any one of claims 1-3, wherein along the longitudinaldirection of the walls the top width b₁ of the sills is smaller than thebottom width b₂ of the sills, and the downstream side is vertical, whilethe upstream side is inclined.
 6. The debris flow drainage canalaccording to claim 3, wherein the angle is within the range of 45° to75°.
 7. The debris flow drainage canal according to claim 4, whereinalong the vertical direction of the walls, the horizontal slope 1:n,which is the sills' height difference h divides the sills' sill(1)'shorizontal length B along the vertical direction of the walls, isbetween 1:4 and 1:20.
 8. The debris flow drainage canal according toclaim 5, wherein the top width b₁ is within the range of 0.6-1.5 m, andthe bottom width b₂ is within the range of 1.0˜2.0 m, and the upstreamside's slope 1:m, which is upstream slope's height H₁ divides (b₂−b₁),is between 1:0.4 and 1:1.
 9. The debris flow drainage canal according toany one of claims 1-3, wherein the space L between each two steps of thesills is within the range of 8.0˜25.0 m, and the embedded depth H of thesills is within the range of 1.5˜2.5 m.
 10. A method of using the debrisflow drainage canal based on scour prevention cascaded sills accordingto claim 1, comprising using the drainage canal to prevent and controldiluted debris flow, water-rock flow and flash floods with longitudinalslope of 3%-12%.